Organic thin-film transistor and fabrication method thereof and organic thin-film device

ABSTRACT

An organic thin-film transistor having a higher carrier-mobility, a method of fabricating the organic thin-film transistor and an organic thin-film device including the organic thin-film transistor are provided. In an organic thin-film transistor having an organic semiconductor layer, the organic semiconductor layer contains a fluorinated acene compound which is represented by a formula of C 4n+2 F 2n+4 , wherein n is an integer of 2 or greater. The fluorinated acene compound is preferably tetradecafluoropentacene or dodecafluoronaphthacene.

TECHNICAL FIELD

The present invention relates to an organic thin-film transistor and amethod of fabricating an organic thin-film transistor and an organicthin-film device.

BACKGROUND ART

In recent years, a study or development for utilizing an organiccompound as a semiconductor material has been actively conducted and astudy intended for utilizing a material of organic compound instead of aconventional device based on silicon is also being paid attention to inthe field of a thin-film transistor (Thin Film Transistor; TFT), whichhas been frequently used for a logic element or a switching element.Since it is easier to process an organic compound compared to silicon asan inorganic substance, it is expected that a low-cost device can berealized by utilizing an organic compound as a semiconductor material.Also, a variety of substrates, which include a plastic substrate, can beused in regard to a semiconductor device utilizing an organic compound,since it is possible to produce the device at temperature of 100° C. orlower. Further, it is expected to realize a flexible device by using aplastic substrate and a semiconductor material of organic compound incombination, since the semiconductor material of organic compound isstructurally flexible.

A typical organic TFT has a substrate, a gate electrode, a gateinsulating film, an organic semiconductor layer, a source electrode anda drain electrode. In such an organic TFT, a gate electrode and a gateinsulating film are provided on a substrate and the gate electrode iscovered with the gate insulating film. An organic semiconductor layer isprovided on the gate insulating film and a source electrode and a drainelectrode are provided on the organic semiconductor layer. Also, thesource electrode and the drain electrode lie adjacent at a small spacingon the organic semiconductor layer. Herein, since the electricalconductivity of the organic semiconductor layer between the sourceelectrode and the drain electrode is changed when a voltage applied tothe gate electrode is changed, the electric current flowing between thesource electrode and the drain electrode can be controlled by adjustingthe gate voltage.

Also, various organic compounds have been suggested for a semiconductormaterial used for an organic TFT. For example, low-molecular-weightmaterials such as copper phthalocyanine and pentacene, origomericmaterials such as α-sexithiophene, and polymeric materials such aspoly(alkylthiophene) have been reported.

Among these materials, acene compounds such as naphthacene and pentaceneare known as p-type organic semiconductor materials having an excellentcharacteristic. These acene compounds are organic compounds of planarmolecule having a spread π-electronic system. Then, a thin film can beformed in which plural planar molecules of the acene compound areoriented such that the molecular axes of the molecules are parallel toeach other. As a result, π-electronic orbitals of the plural moleculesof the acene compound mutually overlap in the directions perpendicularto the molecular planes thereof and the mobility of carriers in theorganic semiconductor material is large in the directions perpendicularto the molecular planes. For example, a high hole-mobility of 0.1cm²V⁻¹s⁻¹ has been reported in regard to a p-type organic TET having anorganic semiconductor layer made of naphthacene (for example, see D. J.Gundlach et al., Appl. Phys. Lett., Vol. 80, pp. 2925-2927 (2002)).Also, a hole-mobility of 1 cm²V⁻¹s⁻¹ or greater, which is the highestamong organic semiconductors, is obtained at room temperature in regardto a p-type organic TFT having an organic semiconductor layer made ofpentacene (for example, see Y. Y. Lin et al., IEEE Electron DeviceLetters, Vol. 18, No. 12, pp. 606-608 (1997)). Particularly, thehole-mobility of the p-type organic TFT having an organic semiconductorlayer made of pentacene is comparable to or greater than anelectron-mobility of amorphous silicon, which has been widely used for aliquid crystal display.

On the other hand, as an n-type organic semiconductor material,fluorinated copper phthalocyanine, naphthalenetetracarbodiimidederivatives, perylene derivatives, etc., are ever known. However, it isdifficult to obtain an n-type organic TFT having a highelectron-mobility compared to an electron-mobility of amorphous siliconusing these materials (for example, see Z. Bao et al., J. Am. Chem.,Soc., Vol. 120, pp. 207-208 (1998), H. E. Katz et al., Nature, Vol. 404,pp. 478-480 (2000), and P. R. L. Malenfant et al., Appl. Phys. Lett.,Vol. 80, pp. 2517-2519 (2002)).

Accordingly, an organic semiconductor material having a highelectron-mobility is also desired in regard to an n-type organic TFT. Inorder to obtain an n-type organic semiconductor material having a highelectron-mobility, it is required to obtain an organic compound ofplanar molecule having a spread π-electronic system similar topentacene, which is a p-type organic semiconductor material having ahigh hole-mobility.

Also, as described above, many of organic semiconductors composed ofplanar molecules having such a spread π-electronic system have differentcarrier-mobilities depending on the orientations of these plural planarmolecules and the orientations of these planar molecules influence theconductivity of carriers in a thin film of organic semiconductor. Forexample, in regard to pentacene having a π-electronic system which is ap-type organic semiconductor material, it is known that a p-type organicsemiconductor material composed of pentacene has a high hole-mobility inthe directions perpendicular to the molecular planes of the molecules byorienting the pentacene so that π-electronic orbitals of the pentacenemutually overlap in the directions perpendicular to the molecular planesthereof. Similarly, in order that an n-type organic semiconductormaterial has a high electron-mobility in the directions perpendicular tothe molecular planes of molecules which compose the organicsemiconductor material, it is preferable to orient these planarmolecules so that π-electronic orbitals of the plural planar moleculesmutually overlap in the directions perpendicular to the molecular planesthereof. That is, in order to improve the electron-mobility of an n-typeorganic TFT, an n-type organic semiconductor material for an activelayer in the organic TFT is preferably a thin film having a goodcrystallizability and an orientation property of a molecule of anorganic semiconductor material, similar to those of pentacene which is ap-type organic semiconductor material.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The object of the present invention is to provide an organic thin-filmtransistor having a higher carrier-mobility, a method of fabricating theorganic thin-film transistor and an organic thin-film device includingthe organic thin-film transistor.

Means for Solving the Problem

The first aspect of the present invention is an organic thin-filmtransistor having an organic semiconductor layer, characterized in thatthe organic semiconductor layer contains a fluorinated acene compoundwhich is represented by a formula of C_(4n+2)F_(2n+4), wherein n is aninteger of 2 or greater.

According to the first aspect of the present invention, an organicthin-film transistor having a higher carrier-mobility can be providedsince the organic semiconductor layer contains a fluorinated acenecompound which is represented by a formula of C_(4n+2)F_(2n+4), whereinn is an integer of 2 or greater.

The second aspect of the present invention is an organic thin-filmtransistor composed of a gate electrode, a source electrode, a drainelectrode, a gate insulating film, and an organic semiconductor layer,characterized in that the organic semiconductor layer contains afluorinated acene compound which is represented by a formula ofC_(4n+2)F_(2n+4), wherein n is an integer of 2 or greater.

According to the second aspect of the present invention, an organicthin-film transistor having a higher carrier-mobility can be providedsince the organic semiconductor layer contains a fluorinated acenecompound which is represented by a formula of C_(4n+2)F_(2n+4), whereinn is an integer of 2 or greater.

The third aspect of the present invention is an organic thin-filmtransistor according to the first or second aspect of the presentinvention, characterized in that plural molecules of the fluorinatedacene compound are oriented so that molecular axes of the molecules areapproximately parallel to each other and a normal direction of amolecular plane of the molecule approximately corresponds to a directionof electric current flowing in the organic semiconductor layer. Herein,the molecular axes of the molecules being approximately parallel to eachother includes the case where the molecular axes of the plural moleculesof the fluorinated acene compound are regarded as being substantiallyparallel to each other in addition to the case where the molecular axesof the plural molecules of the fluorinated acene compound are completelyparallel to each other. Also, approximately corresponding to thedirection of electric current flowing in the organic semiconductor layerincludes the case where the normal direction of the molecular planes ofthe plural molecules of the fluorinated acene compound is regarded assubstantially corresponding to the direction of electric current flowingin the organic semiconductor layer in addition to the case where thenormal direction of the molecular planes of the plural molecules of thefluorinated acene compound completely correspond to the direction ofelectric current flowing in the organic semiconductor layer.

According to the third aspect of the present invention, an organicthin-film transistor having a further higher carrier-mobility can beprovided since plural molecules of the fluorinated acene compound areoriented so that molecular axes of the molecules are approximatelyparallel to each other and a normal direction of a molecular plane ofthe molecule approximately corresponds to a direction of electriccurrent flowing in the organic semiconductor layer.

The fourth aspect of the present invention is an organic thin-filmtransistor according to any of the first through third aspects of thepresent invention, characterized in that the fluorinated acene compoundis tetradecafluoropentacene.

According to the fourth aspect of the present invention, an organicthin-film transistor having a higher carrier-mobility can be morereliably provided since the fluorinated acene compound istetradecafluoropentacene.

The fifth aspect of the present invention is an organic thin-filmtransistor according to any of the first through third aspects of thepresent invention, characterized in that the fluorinated acene compoundis dodecafluoronaphthacene.

According to the fifth aspect of the present invention, an organicthin-film transistor having a higher carrier-mobility can be morereliably provided since the fluorinated acene compound isdodecafluoronaphthacene.

The sixth aspect of the present invention is a method of fabricating anorganic thin-film transistor having a substrate and an organicsemiconductor layer, characterized in that the organic semiconductorlayer is formed by controlling temperature of the substrate to 30° C. orhigher and 65° C. or lower and vacuum-depositingtetradecafluoropentacene on the substrate.

According to the sixth aspect of the present invention, a method offabricating an organic thin-film transistor having a highercarrier-mobility can be provided since the organic semiconductor layeris formed by controlling temperature of the substrate to 30° C. orhigher and 65° C. or lower and vacuum-depositingtetradecafluoropentacene on the substrate.

The seventh aspect of the present invention is a method of fabricatingan organic thin-film transistor having a substrate and an organicsemiconductor layer, characterized in that the organic semiconductorlayer is formed by controlling temperature of the substrate to 24° C. orhigher and 60° C. or lower and vacuum-depositing dodecafluoronaphthaceneon the substrate.

According to the seventh aspect of the present invention, a method offabricating an organic thin-film transistor having a highercarrier-mobility can be provided since the organic semiconductor layeris formed by controlling temperature of the substrate to 24° C. orhigher and 60° C. or lower and vacuum-depositing dodecafluoronaphthaceneon the substrate.

The eighth aspect of the present invention is an organic thin-filmdevice characterized by including an organic thin-film transistoraccording to any of the first through fifth aspects of the presentinvention.

According to the eighth aspect of the present invention, an organicthin-film device can be provided which includes an organic thin-filmtransistor having a higher carrier-mobility since an organic thin-filmtransistor according to any of the first through fifth aspects of thepresent invention is included.

The ninth aspect of the present invention is an organic thin-film deviceaccording to the eighth aspect of the present invention, characterizedby including the organic thin-film transistor which constitutes ann-type thin-film transistor and a p-type thin-film transistor.

According to the ninth aspect of the present invention, various organicthin-film devices can be provided which includes an n-type organicthin-film transistor having a higher carrier-mobility and a p-typethin-film transistor since the organic thin-film transistor whichconstitutes an n-type thin-film transistor and a p-type thin-filmtransistor are included.

The tenth aspect of the present invention is an organic thin-film deviceaccording to the ninth aspect of the present invention, characterized inthat the p-type thin-film transistor has an organic semiconductor layerwhich contains pentacene.

According to the tenth aspect of the present invention, an organicthin-film device can be provided which includes an n-type organicthin-film transistor having a higher carrier-mobility and a p-typethin-film transistor having a high carrier-mobility since the p-typethin-film transistor has an organic semiconductor layer which containspentacene.

Advantageous Effect of the Invention

According to the present invention, an organic thin-film transistorhaving a higher carrier-mobility, a method of fabricating the organicthin-film transistor and an organic thin-film device including theorganic thin-film transistor can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section diagram illustrating one aspect of an organicthin-film transistor of the present invention.

FIG. 2 is a diagram showing an X-ray diffraction pattern of an organicsemiconductor layer made of tetradecafluoropentacene in practicalexample 1.

FIG. 3 is a diagram showing the electric characteristics of an organicTFT having an organic semiconductor layer made oftetradecafluoropentacene in practical example 1.

EXPLANATION OF LETTERS OR NUMERALS

11 substrate

12 gate electrode

13 gate insulating film

14 source electrode

15 drain electrode

16 organic semiconductor layer

BEST MODE FOR CARRYING OUT THE INVENTION

Next, embodiments of the present invention are described with referenceto the drawings.

First, an organic thin-film transistor according to the presentinvention is described. The organic thin-film transistor according tothe present invention has an organic semiconductor layer. The organicsemiconductor layer contains a fluorinated acene compound. Herein, afluorinated acene compound is a compound represented by a formula ofC_(4n+2)F_(2n+4), wherein n is an integer of 2 or greater. That is, afluorinated acene compound is a compound in which all of hydrogen atomsof an acence compound are replaced by fluorine atoms. Herein, an acenecompound represents a hydrocarbon compound in which two or more benzenerings are linearly fused. As specific examples of the fluorinated acenecompound, there can be provided octafluoronaphthalene (n=2, C₁₀F₈),decafluoroanthracene (n=3, C₁₄F₁₀), dodecafluoronaphthacene (n=4,C₁₈F₁₂), tetradecafluoropentacene (n=5, C₂₂F₁₄), hexadecafluorohexacene(n=6, C₂₆F₁₆), and octadecafluoroheptacene (n=7, C₃₀F₁₈), etc. n ispreferably 10 or less.

Such a fluorinated acene compound is an organic compound of a planarmolecule having an extended π-electronic system. Thus, since thefluorinated acene compound is a planar molecule having an extendedπ-electronic system, π-electronic orbitals of plural molecules offluorinated acene compound mutually overlap, whereby carrier-mobilityamong these plural molecules of fluorinated acene compound can beimproved. Particularly, when plural molecules of fluorinated acenecompound are oriented such that molecular axes (a long axis, short axisand normal axis of a molecular plane) of the plural molecules offluorinated acene compound are approximately parallel to each other,that is, such that molecular planes of the plural molecules offluorinated acene compound approximately-parallel-overlap, the overlapof π-electronic orbitals of the plural molecules of fluorinated acenecompound can be enhanced. As a result, the carrier-mobility among theplural molecules of fluorinated acene compound can be more improved.Additionally, the term “approximately parallel” in the claims and thespecification includes to be substantially regarded as being parallel aswell as to be perfectly parallel.

Also, when plural molecules of fluorinated acene compound are orientedsuch that molecular axes of the plural molecules of fluorinated acenecompound are approximately aligned and the normal line of a molecularplane of the molecule of fluorinated acene compound (directionsperpendicular to the molecular plane) is approximately aligned with thedirection of current flowing in an organic semiconductor layer, themobility of a carrier flowing in the organic semiconductor layer can befurther improved. For example, when plural molecules of fluorinatedacene compound are oriented such that molecular planes of the moleculesof fluorinated acence compound are approximately parallel to each otherand long axes of the molecules of fluorinated acene compound aredirected to directions which are approximately perpendicular to asurface of a substrate for an organic thin-film transistor, π-electronicorbitals of these plural molecules overlap along directions which areapproximately parallel to the surface of the substrate and carriersgenerated in the organic semiconductor layer can comparatively easilymove along the directions which are approximately parallel to thesurface of the substrate. Additionally, the term “being approximatelyaligned” in the claims and the specification includes to besubstantially regarded as being aligned as well as to be perfectlyaligned.

Thus, According to the present invention, an organic thin-filmtransistor having a high carrier-mobility (field-effect mobility) can beprovided.

Furthermore, in regard to a fluorinated acene compound, since hydrogenatoms of an acene compound are replaced by fluorine atoms havingelectronegativity higher than that of a hydrogen atom, π-electrondensity of a fluorinated acence compound is smaller than π-electrondensity of an acene compound due to the electron-withdrawing propertiesof fluorine atoms. Accordingly, a fluorinated acene compound has anelectron accepting property higher than that of an acence compound andhas electron conductivity. That is, carriers moving through afluorinated acene compound are electrons and a fluorinated acenecompound is preferably used as an n-type organic semiconductor material.Therefore, a fluorinated acene compound can have a largerelectron-mobility and an n-type organic thin-film transistor having ahigh electron-mobility can be provided by using a fluorinated acenecompound as a material for an organic semiconductor layer.

Specifically, for example, an organic thin-film transistor having anorganic semiconductor layer made of tetradecafluoropentacene as afluorinated acene compound is an n-type organic thin-film transistor andexhibits an electron-mobility of 0.1 cm²/Vs or greater and an on/offratio of current flowing in the organic semiconductor (current flowingbetween a source electrode and a drain electrode) of 10⁴ or greater.That is, an organic thin-film transistor having an organic semiconductorlayer containing a fluorinated acene compound can be an n-type organicthin-film device having a high carrier-mobility comparable to or greaterthan that of a p-type thin-film transistor having an organicsemiconductor layer made of an acene compound such as naphthacene andpentacene.

Herein, the fluorinated acence compound is preferablytetradecafluoropentacene (C₂₂F₁₄). That is, the fluorinated acenecompound is a compound represented by a formula of

wherein this compound is a compound of n=5 among compounds representedby a formula of C_(4n+2)F_(2n+4). The fluorinated acene compound istetradecafluoropentacene, whereby an organic thin-film transistor havinga high carrier-mobility can be more reliably provided.

Additionally, when an organic thin-film transistor having an organicsemiconductor layer made of tetradecafluoropentacene as a fluorinatedacene compound is fabricated, the organic semiconductor layer is formed,preferably, by controlling the temperature of a substrate for theorganic thin-film transistor to 30° C. or higher and 65° C. or lower andvacuum-depositing tetradecafluoropentacene on the substrate. Herein, tovacuum-deposit tetradecafluoropentacene on a substrate includes both todirectly vacuum-deposit tetradecafluoropentacene on a surface of asubstrate so as to directly form a thin film of tetradecafluoropentaceneon the surface of the substrate and to from another layer on a surfaceof a substrate and subsequently vacuum-deposit tetradecafluoropentaceneon a surface of the another layer formed on the substrate so as to forma thin film of tetradecafluoropentacene on the surface of the anotherlayer formed on the substrate. Thus, an organic semiconductor layer inwhich plural molecules of tetradecafluoropentacene are comparativelyuniformly oriented can be obtained by controlling the temperature of asubstrate for an organic thin-film transistor to 30° C. or higher and65° C. or lower and vacuum-depositing tetradecafluoropentacene on thesubstrate so that an organic semiconductor layer made oftetradecafluoropentacene is formed. Also, in this case, molecular planesof plural molecules of tetradecafluoropentacene are approximatelyparallel to each other and a longer axis of the molecule oftetradecafluoropentacene is directed to directions which areapproximately perpendicular to a surface of a substrate for an organicthin-film transistor. Therefore, an organic thin-film transistor havinga high carrier-mobility can be fabricated.

Also, the fluorinated acence compound is preferablydodecafluoronaphthacene (C₁₈F₁₂). That is, the fluorinated acenecompound is a compound represented by a formula of

wherein this compound is a compound of n=4 among compounds representedby a formula of C_(4n+2)F_(2n+4). The fluorinated acene compound isdodecafluoronaphthacene, whereby an organic thin-film transistor havinga high carrier-mobility can be more reliably provided.

Additionally, when an organic thin-film transistor having an organicsemiconductor layer made of dodecafluoronaphthacene as a fluorinatedacene compound is fabricated, the organic semiconductor layer is formed,preferably, by controlling the temperature of a substrate for theorganic thin-film transistor to 24° C. or higher and 60° C. or lower andvacuum-depositing dodecafluoronaphthacene on the substrate. Herein, tovacuum-deposit dodecafluoronaphthacene on a substrate includes both todirectly vacuum-deposit dodecafluoronaphthacene on a surface of asubstrate so as to directly form a thin film of dodecafluoronaphthaceneon the surface of the substrate and to from another layer on a surfaceof a substrate and subsequently vacuum-deposit dodecafluoronaphthaceneon a surface of the another layer formed on the substrate so as to forma thin film of dodecafluoronaphthacene on the surface of the anotherlayer formed on the substrate. Thus, an organic semiconductor layer inwhich plural molecules of dodecafluoronaphthacene are comparativelyuniformly oriented can be obtained by controlling the temperature of asubstrate for an organic thin-film transistor to 24° C. or higher and60° C. or lower and vacuum-depositing dodecafluoronaphthacene on thesubstrate so that an organic semiconductor layer made ofdodecafluoronaphthacene is formed. Also, in this case, molecular planesof plural molecules of dodecafluoronaphthacene are approximatelyparallel to each other and a longer axis of the molecule ofdodecafluoronaphthacene is directed to directions which areapproximately perpendicular to a surface of a substrate for an organicthin-film transistor. Therefore, an organic thin-film transistor havinga high carrier-mobility can be fabricated.

Next, one aspect of an organic thin-film transistor according to thepresent invention and a fabrication method thereof are described withreference to FIG. 1.

FIG. 1 is a cross-section diagram for illustrating one aspect of anorganic thin-film transistor of the present invention. This organicthin-film transistor is an organic thin-film transistor called a generalreverse-stagger-type structure. As shown in FIG. 1, the organicthin-film transistor according to the present invention has a substrate11, a gate electrode 12, a gate insulating-film 13, a source electrode14, a drain electrode 15, and an organic semiconductor layer 16. Morespecifically, the gate electrode 12 and the gate insulating-film 13 areprovided on a surface of the substrate 11 and the gate electrode 12 iscovered with the gate insulating-film 13. The organic semiconductorlayer 16 is provided on the surface of the gate insulating-film 13 atthe opposite side of the gate electrode 12, and the source electrode 14and the drain electrode 15 are provided on the surface of the organicsemiconductor layer at the opposite side of the gate insulating film 13.The source electrode 14 and the drain electrode 15 oppose to each othervia a small gap on the surface of the organic semiconductor layer 16.The channel length and channel width of the organic semiconductor aredetermined depending on the size of gap between the source electrode 14and the drain electrode 15 on the organic semiconductor layer 16.

Also, carriers move through a channel in the organic semiconductor layer16 which channel is provided between the source electrode 14 and thedrain electrode 15 in the organic thin-film transistor shown in FIG. 1.Herein, the movement of carriers through the channel formed in theorganic semiconductor layer 16 can be controlled by adjusting a voltageapplied to the gate electrode 12. In the organic thin-film transistoraccording to the present invention, carriers moving in the organicsemiconductor layer are electrons since the organic semiconductor layercontains a fluorinated acene compound, and the flow of electrons(electric current) moving in the organic semiconductor layer iscontrolled by applying a positive voltage to the gate electrode. Thatis, the organic thin-film transistor according to the present inventionis an n-type organic thin-film transistor.

As a general method for fabricating the organic thin-film transistoraccording to the present invention which is shown in FIG. 1, the organicthin-film transistor can be obtained by stacking thin films of the gateelectrode 12, gate insulating-film 13, organic semiconductor layer 16containing a fluorinated acene compound and source electrode 14 anddrain electrode 15 on the substrate 11 in order.

As a material of the substrate 11, an inorganic material such as glass,quartz, silicon, metals and ceramics and an organic material such asplastics can be used. Herein, when an electrically conductive materialsuch as metals is used as a material of the substrate 11, the substrate11 can effect the function of a gate electrode and, therefore, thefabrication of another gate electrode 12 on the substrate 11 having thefunction of a gate electrode 12 can be omitted. The organic thin-filmtransistor according to the present invention is an MIS(metal-insulator-semiconductor)-type thin-film transistor composed ofthe gate electrode 12, the gate insulating-film 13, the source electrode14, the drain electrode 15 and the organic semiconductor layer 16containing a fluorinated acene compound. Such a MIS-type thin-filmtransistor exhibits a good characteristic of n-type organic thin-filmtransistor and can be easily fabricated at a low cost because of needingno other substrates. Also, when a plastic substrate is used as amaterial of the substrate 11, the entire of an organic thin-filmtransistor including a plastic substrate can have flexibility and,therefore, the organic thin-film transistor according to the presentinvention can be used in various organic thin-film devices such asdriving circuits for a flexible display, IC cards such as credit cards,and ID tags adhering to and used for a commercial product. However, itis necessary for a plastic material used for the plastic substrate to beexcellent in heat resistance, dimensional stability, solvent resistance,an electrical insulating property, processibility, low gas permeability,and low hygroscopicity. As such a plastic material, for example,poly(ethyleneterephthalate), poly(ethylenenaphthalate), poly(styrene),polycarbonates, polyallylates, and polyimides can be provided.

Next, as a material of the gate electrode 12, there can be providedmetals such as gold, platinum, chromium, tungsten, tantalum, nickel,copper, aluminum, silver, magnesium, and calcium and alloys of thesemetals, and polysilicon, amorphous silicon, graphite, indium tin oxide(ITO), zinc oxide, and electrically conductive polymers. The gateelectrode 12 is formed by means of a well-known method such as a vacuumdeposition method, an electron beam deposition method, an RF sputteringmethod, and a printing method, using the material of the gate electrode12.

Next, as a material of the gate insulting-film 13, there can be providedmaterials such as SiO₂, Si₃N₄, SiON, Al₂O₃, Ta₂O₅, amorphous silicon,polyimide resins, poly(vinylphenol) resin, poly(para-xylylene) resin,and poly(methyl methacrylate) resin. The gate insulating-film 13 isformed by means of a well-known film formation method similar to thosefor the gate electrode 12, while one kind of material selected from theabove-mentioned materials is used, or formed by means of a well-knownfilm formation method similar to those for the gate electrode 12, whiletwo or more kinds of materials selected from the above-mentionedmaterials are mixed.

Next, the organic semiconductor layer (organic active layer) 16 isformed by means of a well-known film fabrication method such as a vacuumdeposition method, using the above-mentioned fluorinated acene compound.

Finally, as materials of the source electrode 14 and drain electrode 15,there can be provided metals such as gold, platinum, chromium, tungsten,tantalum, nickel, copper, aluminum, silver, magnesium, and calcium andalloys of these metals, and materials such as polysilicon, amorphoussilicon, graphite, indium tin oxide (ITO), zinc oxide, and electricallyconductive polymers. The source electrode 14 and the drain electrode 15are (preferably, simultaneously) formed by means of a well-known filmformation method similar to those for the gate electrode 12, using thematerials of the source electrode 14 and drain electrode 15.

Further, it is preferable to provide a moisture permeation preventinglayer (gas barrier layer) on the surface of the substrate 11 at the sameside of the gate electrode 12, the surface of the substrate 11 at theopposite side of the gate electrode 12, or both of them. Thus, thepenetration of water content and/or oxygen in air into an organicsemiconductor layer can be prevented by providing a moisture permeationpreventing layer on the substrate 11. As a result, rapid reduction ofthe life time of the organic semiconductor layer can be prevented. As amaterial for such a moisture permeation preventing layer, it ispreferable to use an inorganic material such as silicon nitride andsilicon oxide. Also, the moisture permeation preventing layer isfilm-formed by the means of a well-known method such as a high-frequencysputtering method.

In addition, in an organic thin-film transistor according to the presentinvention, a protective layer such as a hard coat layer and an undercoat layer may be provided on the substrate 11 according to needs.

Next, a method for synthesizing a fluorinated acene compound used for anorganic thin-film transistor according to the present invention isdescribed.

Generally, a fluorinated acene compound represented by a formula ofC_(4n+2)F_(2n+4) wherein n is an integer of 2 or greater is synthesizedfrom a compound in which a part of hydrogen atoms of an acene compoundis replaced by a fluorine atom and the residual hydrogen atom(s) of theacene compound is replaced by a functional group containing an oxygenatom. Therefore, a functional group containing an oxygen atom isintroduced to a carbon atom in the skeleton of the acene compound at adesired position, according to need. Herein, the functional groupcontaining an oxygen atom includes an oxo group (an oxygen atom of acarbonyl group), a hydroxyl group, or an alkoxy group. Next, thefunctional group containing an oxygen atom in the skeleton of the acenecompound is replaced by two fluorine atoms through fluoridationreaction. Then, one of the two fluorine atoms is eliminated from thecarbon atom of the skeleton of the acene compound to which the twofluorine atoms bond, through partial defluoridation reaction, whereby adesired fluorinated acene compound can be obtained.

Next, as an example of a synthesis method for a fluorinated acenecompound, a synthesis method for tetradecafluoropentacene(perfluoropentacene) is described in more detail.

First, as shown in scheme 1,

compound (1) and compound (2) are reacted under the presence of a Lewisacid so as to obtain compound (3). That is,5,6,7,8-tetrafluoro-9,10-dihydroxyanthracene-1,4-dione (1) is reactedwith 4,5,6,7-tetrafluoroisobenzfuran-1,3-dione (2) so as to obtain1,2,3,4,8,9,10,11-octafluoro-5,7,12,14-tetrahydroxypentacene-6,13-dione(3). Additionally, the Lewis acid may be used in combination with sodiumchloride.

The Lewis acid used in scheme 1 is not particularly limited and, forexample, aluminum chloride, zinc chloride, iron (III) chloride, tin (IV)chloride and a boron trifluoride ether complex can be used, and aluminumchloride is preferable. The quantity of the used Lewis acid is 0.1equivalents or more and 5.0 equivalents or less, preferably 0.2equivalents or more and 5.0 equivalents or less, to the quantity of theraw materials. When sodium chloride is used with the Lewis acid, thequantity of the used sodium chloride is 0.1 equivalents or more and 10.0equivalents or less, preferably 5.0 equivalents or more and 7.0equivalents or less, to the quantity of the raw materials. The quantityof the used compound (2) is 1.0 equivalent or more and 5.0 equivalentsor less, preferably 1.1 equivalents or more and 2.0 equivalents or less,to the quantity of the compound (1). The reaction temperature is 0° C.or higher and 320° C. or lower, preferably 200° C. or higher and 300° C.or lower. The reaction time is preferably 1 hour or longer and 10 hoursor shorter. After the completion of the reaction, the objective compound(3) can be obtained by conducting a common post-treatment and performingpurification.

Next, as shown in scheme 2

compound (3) is reacted with a fluoridating agent so that it isfluoridated so as to obtain compound (4). That is,1,2,3,4,8,9,10,11-octafluoro-5,7,12,14-tetrahydroxypentacene-6,13-dione(3) is reacted with a fluoridating agent so as to obtain1,2,3,4,5,5,6,6,7,7,8,9,10,11,12,12,13,13,14,14-icosafluoro-5,6,7,12,13,14-hexahydropentacene(4).

The fluoridating agent used in scheme 2 is not particularly limited andeach kind of fluoride can be used, and it is preferably a fluoride of aGroup 15 element or a Group 16 element, more preferably sulfurtetrafluoride. The preferable quantity of the used sulfur tetrafluorideis 4.0 times or greater and 30.0 times or less of the mole quantity ofthe raw materials. One of these fluoridating agents may be singularlyused and the plural fluoridating agents may be used in combination. Forexample, a mixture of sulfur tetrafluoride and hydrogen fluoride can beused. When the reaction is carried out under pressure, hydrogen fluoridealso acts as a solvent. In the fluoridation process, only the rawmaterials and the fluoridating agent may be used or another substancemay coexist in the reaction system. As another substance coexisting inthe reaction system, a substance which acts as a solvent or a catalystcan be selected. The substance acting as a solvent is not particularlylimited except that it is a substance which is liquid under the reactioncondition(s), and hydrogen fluoride and a fluorine-containing solventsuch as dichloromethane and chloroform can be provided. When hydrogenfluoride is used, the quantity of the used hydrogen fluoride ispreferably 1 mL or more and 20 mL or less to 1 g of the raw materials.The fluoridation process may be carried out at a normal pressure but,when the reaction system is heated, it is preferable to perform heatingunder pressure. Preferably, the reaction pressure is in a range of 0 MPaor higher and 20 MPa or lower, the reaction temperature is in a range of−40° C. or higher and 320° C. or lower, and the reaction time is in arange of 2 hours or longer and 150 hours or shorter. After thecompletion of the fluoridation reaction, the objective compound (4) canbe obtained by conducting a common post-treatment and subsequentlyperforming purification. As a purification method, a conventionalpublicly-known method can be used in which solvent extraction andrecrystallization are included. In scheme 2, the objective compound (4)can be obtained by performing solvent extraction with an organic solventsuch as chloroform and further performing recrystallization.

Finally, as shown in scheme 3,

compound (4) is reacted with a reducing agent so as to obtain compound(5). That is,1,2,3,4,5,5,6,6,7,7,8,9,10,11,12,12,13,13,14,14-icosafluoro-5,6,7,12,13,14-hexahydropentacene(4) is reacted with a reducing agent so that it is partiallydefluoridated so as to obtain tetradecafluoropentacene(perfluoropentacene) (5).

The reducing agent used in the defluoridation process is notparticularly limited and a general reducing agent is used. As a reducingagent, for example, there can be provided Group 1 elements such aslithium, sodium, potassium, rubidium and cesium; Group 2 elements suchas beryllium, magnesium, calcium, strontium and barium; Group 3 elementssuch as scandium, yttrium and lanthanoids; Group 4 elements such astitanium, zirconium and hafnium; Group 5 elements such as vanadium,niobium and tantalum; Group 6 elements such as chromium, molybdenum andtungsten; Group 7 elements such as manganese and rhenium; Group 8elements such as iron, ruthenium and osmium; Group 9 elements such ascobalt, rhodium and iridium; Group 10 elements such as nickel, palladiumand platinum; Group 11 elements such as copper, silver and gold; Group12 elements such as zinc, cadmium and mercury; Group 13 elements such asboron, aluminum, indium, gallium and thallium; Group 14 elements such ascarbon, silicon, germanium, tin and lead; Group 15 elements such asphosphorus, arsenic, antimony and bismuth; Group 16 elements such assulfur, selenium and tellurium; sodium oxalate; activated carbon; andsamarium iodide, and it is preferably zinc, iron, copper, nickel orpalladium, more preferably zinc. One of these reducing agents may besingularly used or the plural reducing agents may be used incombination. When zinc is used, the quantity of the used zinc is 6.0equivalents or more and 200 equivalents or less, preferably 50equivalents or more and 100 equivalents or less, to the quantity of theraw materials. It is preferable to carry out the defluoridation reactionunder atmosphere of an inert gas such as nitrogen, helium, neon, andargon, or under vacuum. The reaction temperature is 0° C. or higher and600° C. or lower, preferably 200° C. or higher and 300° C. or lower. Thereaction time is preferably 2 hours or longer and 24 hours or shorter.The defluoridation process may be carried out using only the rawmaterials and the reducing agent or another substance may coexist in thereaction system. As another substance coexisting in the reaction system,a substance which acts as a solvent or a catalyst can be selected. Forexample, the raw materials may be reacted with samarium iodide, zinc,sodium-benzophenone, or the combination thereof in an organic solvent.As an organic solvent, for example, N,N-diethylformamide andtetrahydrofuran can be provided. After the completion of thedefluoridation reaction, the objective compound (5) can be obtained byconducting a common post-treatment and subsequently performingpurification. As a purification method, a conventional publicly-knownmethod can be used in which solvent extraction, recrystallization andsublimation are included.

Next, as an example of a synthesis method for a fluorinated acenecompound, a synthesis method for dodecafluoronaphthacene is described inmore detail.

First, as shown in scheme 4,

compound (6) is reacted with compound (2) under the presence of a Lewisacid so as to obtain compound (7). That is,1,2,3,4-tetrafluoro-5,8-dimethoxynaphthalene (6) is reacted with4,5,6,7-tetrafluoroisobenzfuran-1,3-dione (2) under the presence of aLewis acid so as to obtain1,2,3,4,7,8,9,10-octafluoro-6,11-dihydroxynaphthacene-5,12-dione (7).Additionally, the Lewis acid may be used in combination with sodiumchloride.

The Lewis acid used in scheme 4 is not particularly limited and, forexample, aluminum chloride, zinc chloride, iron (III) chloride, tin (IV)chloride and a boron trifluoride ether complex can be used, and aluminumchloride is preferable. The quantity of the used Lewis acid is 0.1equivalents or more and 5.0 equivalents or less, preferably 0.2equivalents or more and 5.0 equivalents or less, to the quantity of theraw materials. When sodium chloride is used with the Lewis acid, thequantity of the used sodium chloride is 0.1 equivalents or more and 10.0equivalents or less, preferably 5.0 equivalents or more and 7.0equivalents or less, to the quantity of the raw materials. The quantityof the used compound (2) is 1.0 equivalent or more and 5.0 equivalentsor less, preferably 1.1 equivalents or more and 2.0 equivalents or less,to the quantity of the compound (6). The reaction temperature is 0° C.or higher and 320° C. or lower, preferably 200° C. or higher and 300° C.or lower. The reaction time is preferably 1 hour or longer and 10 hoursor shorter. After the completion of the reaction, the objective compound(7) can be obtained by conducting a common post-treatment and performingpurification.

Next, as shown in scheme 5,

compound (7) is reacted with a fluoridating agent so that it isfluoridated so as to obtain compound (8) and compound (9). That is,1,2,3,4,7,8,9,10-octafluoro-6,11-dihydroxynaphthacene-5,12-dione (7) isreacted with a fluoridating agent so as to obtain1,2,3,4,5,5,6,6,7,8,9,10,11,11,12,12-hexadecafluoro-5,6,11,12-tetrahydronaphthacene(8) and1,2,3,4,5,5,6,7,8,9,10,11,12,12-tetradecafluoro-5,12-dihydronaphthacene(9).

The fluoridating agent used in scheme 5 is not particularly limited andeach kind of fluoride can be used, and it is preferably a fluoride of aGroup 15 element or a Group 16 element, more preferably sulfurtetrafluoride. The preferable quantity of the used sulfur tetrafluorideis 4.0 times or greater and 30.0 times or less, preferably 10 times orgreater and 20 times or less, of the mole quantity of the raw materials.One of these fluoridating agents may be singularly used and the pluralfluoridating agents may be used in combination. For example, a mixtureof sulfur tetrafluoride and hydrogen fluoride can be used. When thereaction is carried out under pressure, hydrogen fluoride also acts as asolvent. In the fluoridation process, only the raw materials and thefluoridating agent may be used or another substance may coexist in thereaction system. As another substance coexisting in the reaction system,a substance which acts as a solvent or a catalyst can be selected. Thesubstance acting as a solvent is not particularly limited except that itis a substance which is liquid under the reaction condition(s), andhydrogen fluoride and a fluorine-containing solvent such asdichloromethane and chloroform can be provided. When hydrogen fluorideis used, the quantity of the used hydrogen fluoride is preferably 1 mLor more and 20 mL or less to 1 g of the raw materials. The fluoridationprocess may be carried out at a normal pressure but, when the reactionsystem is heated, it is preferable to perform heating under pressure.Preferably, the reaction pressure is in a range of 0 MPa or higher and20 MPa or lower, the reaction temperature is in a range of −40° C. orhigher and 320° C. or lower, and the reaction time is in a range of 2hours or longer and 150 hours or shorter. After the completion of thefluoridation reaction, the objective compounds (8) and (9) can beobtained by conducting a common post-treatment and subsequentlyperforming purification. As a purification method, a conventionalpublicly-known method can be used in which solvent extraction,recrystallization and sublimation are included. In scheme 5, theobjective compounds (8) and (9) can be obtained by performingsublimation under vacuum.

Finally, as shown in scheme 6

and scheme 7,

compounds (8) and/or (9) are/is reacted with a reducing agent so as toobtain compound (10). That is, as shown in scheme 6,1,2,3,4,5,5,6,6,7,8,9,10,11,11,12,12-hexadecafluoro-5,6,11,12-tetrahydronaphthacene(8) is reacted with a reducing agent so that it is partiallydefluoridated so as to obtain dodecafluoronaphthacene (10). Also, sshown in scheme 7,1,2,3,4,5,5,6,7,8,9,10,11,12,12-tetradecafluoro-5,12-dihydronaphthacene(9) is reacted with a reducing agent so that it is partiallydefluoridated so as to obtain dodecafluoronaphthacene (10).

Additionally, in the case of performing a defluoridation process,purified materials of the compounds (8) and (9) as raw materials may beused or an unpurified mixture may be used. Specifically, after compound(6) and a reaction mixture obtained by the reaction of sulfurtetrafluoride(1,2,3,4,5,5,6,6,7,8,9,10,11,11,12,12-hexadecafluoro-5,6,11,12-tetrahydronaphthacene(8) and1,2,3,4,5,5,6,7,8,9,10,11,12,12-tetradecafluoro-5,12-dihydronaphthacene(9)) are solvent-extracted, extracts may be directly used for thedefluoridation process.

The reducing agent used in the defluoridation process is notparticularly limited and a general reducing agent is used. As a reducingagent, for example, there can be provided Group 1 elements such aslithium, sodium, potassium, rubidium and cesium; Group 2 elements suchas beryllium, magnesium, calcium, strontium and barium; Group 3 elementssuch as scandium, yttrium and lanthanoids; Group 4 elements such astitanium, zirconium and hafnium; Group 5 elements such as vanadium,niobium and tantalum; Group 6 elements such as chromium, molybdenum andtungsten; Group 7 elements such as manganese and rhenium; Group 8elements such as iron, ruthenium and osmium; Group 9 elements such ascobalt, rhodium and iridium; Group 10 elements such as nickel, palladiumand platinum; Group 11 elements such as copper, silver and gold; Group12 elements such as zinc, cadmium and mercury; Group 13 elements such asboron, aluminum, indium, gallium and thallium; Group 14 elements such ascarbon, silicon, germanium, tin and lead; Group 15 elements such asphosphorus, arsenic, antimony and bismuth; Group 16 elements such assulfur, selenium and tellurium; sodium oxalate; activated carbon; andsamarium iodide, and it is preferably zinc, iron, copper, nickel orpalladium, more preferably zinc. One of these reducing agents may besingularly used or the plural reducing agents may be used incombination. When zinc is used, the quantity of the used zinc is 6.0equivalents or more and 200 equivalents or less, preferably 50equivalents or more and 100 equivalents or less, to the quantity of theraw materials. It is preferable to carry out the defluoridation reactionunder atmosphere of an inert gas such as nitrogen, helium, neon, andargon, or under vacuum. The reaction temperature is 0° C. or higher and600° C. or lower, preferably 200° C. or higher and 300° C. or lower. Thereaction time is preferably 2 hours or longer and 24 hours or shorter.The defluoridation process may be carried out using only the rawmaterials and the reducing agent or another substance may coexist in thereaction system. As another substance coexisting in the reaction system,a substance which acts as a solvent or a catalyst can be selected. Forexample, the raw materials may be reacted with samarium iodide, zinc,sodium-benzophenone, or the combination thereof in an organic solvent.As an organic solvent, for example, N,N-diethylformamide andtetrahydrofuran can be provided. After the completion of thedefluoridation reaction, the objective compound (10) can be obtained byconducting a common post-treatment and subsequently performingpurification. As a purification method, a conventional publicly-knownmethod can be used in which solvent extraction, recrystallization andsublimation are included.

Next, an organic thin-film device according to the present invention isdescribed. The organic thin-film device according to the presentinvention includes an organic thin-film transistor according to thepresent invention, that is, an organic thin-film transistor having anorganic semiconductor layer containing a fluorinated acene compound.Therefore, according to the present invention, an organic thin-filmdevice which includes an organic thin-film transistor having a highcarrier-mobility can be provided.

Preferably, an organic thin-film device according to the presentinvention has an organic thin-film transistor according to the presentinvention which is configured as an n-type thin-film transistor and ap-type thin-film transistor. That is, the organic thin-film deviceaccording to the present invention has the n-type thin-film transistorand the p-type thin-film transistor, wherein the n-type thin-filmtransistor has an organic semiconductor layer containing a fluorinatedacene compound. In this case, various organic thin-film devices can beprovided which include an n-type organic thin-film transistor having ahigh electron-mobility and a p-type thin-film transistor. For example,an n-type thin-film transistor having an organic semiconductor layercontaining a fluorinated acene compound and a p-type thin-filmtransistor are connected to each other so that various logic elements orswitching elements can be formed. As such a logic element, for example,there can be provided publicly-known logic elements such as an invertercircuit in which one n-type thin-film transistor and one p-typethin-film transistor are connected in series, a NAND circuit which iscomposed of two n-type thin-film transistors in series and two p-typethin-film transistors in parallel, and a NOR circuit which is composedof two n-type thin-film transistors in parallel and two p-type thin-filmtransistors in series. Also, as a switching element, there can beprovided a publicly-known switching element such as an inverter circuitin which one n-type thin-film transistor and one p-type thin-filmtransistor are connected in series, etc.

Also, a p-type thin-film transistor included in an organic thin-filmdevice according to the present invention preferably has an organicsemiconductor layer containing pentacene. In this case, since theorganic thin-film device has an n-type thin-film transistor which has anorganic semiconductor layer containing a fluorinated acene compound anda p-type thin-film transistor which has an organic semiconductor layercontaining pentacene, a high-performance organic thin-film device can beprovided by using an n-type organic thin-film transistor having a highelectron-mobility and a p-type thin-film transistor having a highhole-mobility. That is, as described above, various high-performancelogic elements and switching elements can be formed by connecting then-type thin-film transistor which has an organic semiconductor layercontaining a fluorinated acene compound and the p-type thin-filmtransistor which has an organic semiconductor layer containing pentaceneto each other.

PRACTICAL EXAMPLE 1

{1} Synthesis of tetradecafluoropentacene

First, tetradecafluoropentacene was synthesized by the followingprocedures.

{1-1} First,1,2,3,4,8,9,10,11-octafluoro-5,7,12,14-tetrahydroxypentacene-6,13-dione(3) was synthesized from5,6,7,8-tetrafluoro-9,10-dihydroxy-2,3-dihydroanthracene-1,4-dione (1)and 4,5,6,7-tetrafluoroisobenzofuran-1,3-dione (2).

5,6,7,8-tetrafluoro-9,10-dihydroxy-2,3-dihydroanthracene-1,4-dione (1)(9.84 g, 31.3 mmol), 4,5,6,7-tetrafluoroisobenzofuran-1,3-dione (2)(5.75 g, 26.1 mmol), aluminum chloride (1.53 g, 11.5 mmol), and sodiumchloride (10.0 g, 171 mmol) were thrown into a 200 mL autoclave made ofSUS and heating was made at 280° C. for 1 hour. After the completion ofthe reaction, cooling was made down to room temperature, the reactionmixture was poured into dilute hydrochloric acid, and stirring was madeat 100° C. for 1 hour. Subsequently, the mixture was filtered and theresidue was washed with methanol, dichloromethane, toluene and ether inorder. The obtained solid was vacuum-dried so as to obtain 11.5 g (yieldof 85%) of1,2,3,4,8,9,10,11-octafluoro-5,7,12,14-tetrahydroxypentacene-6,13-dione(3).

Melting point: 300° C. (decomposition)

Mass spectrometry (MS m/z) 516 (M⁺, 100), 258 (29)

Elemental analysis

Calculated values for C₂₂H₄F₈O₆: C, 51.18, H, 0.78

Found values: C, 51.40, H, 1.07

{1-2} Next,1,2,3,4,5,5,6,6,7,7,8,9,10,11,12,12,13,13,14,14-icosafluoro-5,6,7,12,13,14-hexahydropentacene(4) was synthesized from the obtained1,2,3,4,8,9,10,11-octafluoro-5,7,12,14-tetrahydroxypentacene-6,13-dione(3).

The obtained1,2,3,4,8,9,10,11-octafluoro-5,7,12,14-tetrahydroxypentacene-6,13-dione(3) (5 g, 9.68 mmol) was thrown into a 500 mL autoclave made of SUS, thecontainer was cooled down to −78° C., hydrogen fluoride (100 g) wasadded, and, continuously, sulfur tetrafluoride (25 g, 231 mmol) wasadded. Subsequently, the mixture was heated up to 150° C. on thecondition of sealing the reactor. At this time, the pressure in thereactor reached at 4.0 MPa (gage pressure). After the reaction was madefor 96 hours, the reactor was gradually cooled down to room temperatureand a low boiling point compound was slowly disposed to an exclusiondevice. When the internal pressure reached at normal pressure, nitrogenwas introduced into the container so that all the remaining hydrogenfluoride was removed. Afterward, the reaction product (6.6 g) wasextracted with 600 mL of heated chloroform and filtered and,subsequently, the solution was concentrated so as to obtain 4.8 g of acrude product of compound (4). This was recrystallized in chloroform, soas to obtain 2.5 g (3.87 mmol, yield of 40%) of a purified compound (4).

Melting point: 267-269° C.

¹⁹F NMR (188 MHz, solvent: CDCl₃, reference material: C₆F₆)

δ 70.91-70.73 (m, 8F), 61.64-64.46 (m, 4F), 25.86-25.66 (m, 4F), 16.70(d, J=12.8 Hz, 4F)

Mass spectrometry (MS m/z): 644 (M⁺, 100), 625 (M⁺—F, 32), 575 (M⁺—CF₃,77.2)

Elemental analysis

Calculated values for C₂₂F₂₀: C, 41.02

Found values: C, 40.96

{1-3} Finally, tetradecafluoropentacene was synthesized from theobtained1,2,3,4,5,5,6,6,7,7,8,9,10,11,12,12,13,13,14,14-icosafluoro-5,6,7,12,13,14-hexahydropentacene(4).

A mixture of the obtained1,2,3,4,5,5,6,6,7,7,8,9,10,11,12,12,13,13,14,14-icosafluoro-5,6,7,12,13,14-hexahydropentacene(4) (1.23 g, 1.91 mmol) and zinc (10.8 g, 165 mmol) was put into a glasstube (length of 100 mm, outer diameter of 26 mm), and the tube wassealed under vacuum and heated at 230° C. for 30 minutes andcontinuously at 280° C. for 3 hours. The reaction mixture in 20%hydrochloric acid was stirred for 8 hours. The obtained suspension wasfiltered and the residual solid was washed with a dilute hydrochloricacid, water and methanol in order, so as to obtain a dark blue solid.The obtained solid was sublimed at 280° C. under vacuum so as to obtain663 mg (1.25 mmol, yield of 65%) of tetradecafluoropentacene (5).

Mass spectrometry (MS m/z): 530 (M⁺, 100), 499 (M⁺—CF, 25), 265 (51)

Elemental analysis

Calculated values for C₂₂F₁₄: C, 49.84

Found values: C, 49.56

Additionally, in the above-mentioned synthesis oftetradecafluoropentacene, B-540 type of Büchi Company was used for themeasurements of melting point. For the NMR, Gemini 200 NMR Spectrometerof Varian Company was used. For the mass spectrometry, GCMS-QP5050A ofShimadzu Corporation was used. For the elemental analysis, CHN coderMT-6 type of Yanaco was used.

{2} Fabrication of an Organic TFT Having an Organic Semiconductor LayerMade of tetradecafluoropentacene

As a substrate for an organic TFT, a silicon wafer was used on thesurface of which thermally oxidized silicon with a film thickness of 200nm was formed. Herein, for the silicon wafer, a low resistive siliconwafer was used, and a silicon layer on the substrate also functioned asa gate electrode of the organic TFT. After the substrate was washed withorganic solvents such as acetone and isopropyl alcohol, the substratewas further washed by using an ultraviolet-ray-ozone washer. Also,according to need, the substrate was subjected to surface treatment byusing octadecyltrichlorosilane (OTS).

Next, the oxidized silicon film on the substrate was used as a gateinsulating-film and an organic semiconductor layer made oftetradecafluoropentacene was formed on the oxidized silicon film bymeans of a vacuum deposition method using tetradecafluoropentacenesynthesized in {1}. Herein, the organic semiconductor layer made oftetradecafluoropentacene was formed under the following conditions. Thedegree of vacuum in a chamber of the apparatus used in regard to thevacuum deposition method was 1×10⁻⁴ pascals or lower. The temperature ofthe substrate was in a range of room temperature (24° C.) or higher and80° C. or lower. The tetradecafluoropentacene purified by means ofsublimation was thrown into a crucible made of carbon and thetetradecafluoropentacene was heated by using a tantalum wire filamentwinding around the crucible. The deposition rate of the organicsemiconductor layer was 0.3 angstroms/second or higher and 0.5angstroms/second or lower and the film thickness was approximately 35nm.

Finally, gold layers with a film thickness of 50 nm were film-formed onthe organic semiconductor layer by means of a vacuum deposition methodusing a metal-mask, so as to form a source electrode and a drainelectrode. Herein, the channel width and channel length of an organicTFT obtained by forming the source electrode and the drain electrodewere 50 μm or greater and 200 μm or less, and 1,000 μm, respectively.

Thus, the organic TFT having an organic semiconductor layer made oftetradecafluoropentacene as shown in FIG. 1 could be fabricated.

{3} Measurement for the Organic TFT Having an Organic SemiconductorLayer Made of tetradecafluoropentacene

X-ray crystallographic analysis was performed for the organicsemiconductor layer made of tetradecafluoropentacene fabricated in {2}was performed. An X-ray diffraction pattern in regard to the organicsemiconductor layer made of tetradecafluoropentacene is shown in FIG. 2.Herein, the horizontal axis of FIG. 2 denotes a diffraction angle 2θ ofX-rays when the angle of a horizontal direction to the substrate is 0°(wherein θ is an incident angle of the X-ray to the substrate) and thevertical axis denotes intensity of diffracted X-rays. Additionally, theX-ray used for the measurement of an X-ray diffraction pattern was aCu—Kα line with a wavelength of 5.14 angstroms. Three diffractionpatterns in FIG. 2 correspond to substrate temperatures of 25° C., 50°C., and 70° C. when tetradecafluoropentacene was vacuum-deposited,respectively. The primary peak of the X-ray diffraction pattern wasobtained at a diffraction angle of 5.6°, the secondary peak was obtainedat 11.3°, and the tertiary peak was obtained at 17.0°. Since thesediffraction angles corresponded to an intermolecular space of 15.8angstroms, it could be confirmed that the long axis directions ofmolecules of tatradecafluoropentacene were oriented along the verticaldirections to the surface of the substrate. Such a molecular orientationof tetradecafluoropentacene is preferable, since π-electronic orbitalsof the molecules overlap with each other in directions parallel to thesurface of the substrate. Accordingly, it is deduced that carriersinduced in the organic semiconductor layer can comparatively easily moveto the directions parallel to the surface of the substrate. Also, it canbe understood that a thin film of tetradecafluoropentacene in which thelong axis directions of the molecule are directed to the verticaldirections to the surface of the substrate is preferable for an organicsemiconductor layer of an organic TFT, since a direction in which theπ-electronic orbitals of the molecules of tetradecafluoropenatceneoverlap with each other corresponds to the direction of carrier movementfrom the source electrode to the drain electrode in the organic TFTshown in FIG. 1. Also, it can be understood that the spaces betweenmolecules of tetradecafluoropentacene are comparatively uniform in athin film of tetradecafluoropentacene fabricated by controlling thetemperature of the substrate to approximately 30° C. or higher andapproximately 65° C. or lower, since the peak intensity of the X-raydiffraction pattern is comparatively strong and the peak half-valuewidth is comparatively small.

Next, the electrical characteristics of the organic TFT having anorganic semiconductor layer made of tetradecafluoropentacene fabricatedin {2} are shown in FIG. 3. Herein, the horizontal axis of FIG. 3denotes a drain voltage (V) and the vertical axis denotes a draincurrent (A). A change in the drain current versus the drain voltagedepends on a gate voltage V_(g) (V). For each gate voltage, a curve inregard to the change in the drain current versus the drain voltage has alinear region (voltage-proportional region) for low drain voltages and asaturation region for high drain voltages. In addition, when a positivegate voltage applied to the gate electrode is increased, a positivedrain current is also increased, and, therefore, it can be confirmedthat the organic TFT having an organic semiconductor layer made oftetradecafluoropentacene fabricated in {2} was an n-type organic TFT.Further, the field-effect mobility μ of carrier of the organic TFT canbe calculated by using a formulaId=(W/2L)μCi(V_(g)−V_(t))²   (A)which represents a drain current Id in a saturation region of theelectrical characteristics of an organic TFT. Herein, L and W are thegate length and gate width of the organic TFT, respectively, Ci is acapacitance per unit surface area of the gate insulating film, V_(g) isa gate voltage and V_(t) is a threshold voltage of the gate voltage. Thefield-effect mobility of carrier of the organic TFT having an organicsemiconductor layer made of tetradecafluoropentacene fabricated in {2}was calculated by using the formula (A) and, as a result, thefield-effect mobility of carrier of the organic TFT having an organicsemiconductor layer made of tetradecafluoropentacene fabricated at asubstrate temperature of 50° C. was 0.1 cm²/Vs.

PRACTICAL EXAMPLE 2

{1} Synthesis of dodecafluoronaphthacene

First, dodecafluoronaphthacene was synthesized by the followingprocedures.

{1-1} First,1,2,3,4,7,8,9,10-octafluoro-6,11-tetrahydroxynaphthacene-5,12-dione (7)was synthesized from 1,2,3,4-tetrafluoro-5,8-dimethoxynaphthalene (6)and 4,5,6,7-tetrafluoroisobenzofuran-1,3-dione (2).

1,2,3,4-tetrafluoro-5,8-dimethoxynaphthalene (6) (4.77 g, 18.3 mmol),4,5,6,7-tetrafluoroisobenzofuran-1,3-dione (2) (4.77 g, 21.7 mmol),aluminum chloride (23.1 g, 173 mmol), and sodium chloride (3.56 g, 60.9mmol) were thrown into a 200 mL autoclave and heating was made at 200°C. for 1 hour. After the completion of the reaction, cooling was madedown to room temperature, the reaction mixture was poured into dilutehydrochloric acid, and stirring was made at 100° C. for 1 hour.Subsequently, the mixture was filtered and the residue was washed withwater, methanol and ether in order. The obtained solid wasrecrystallized from dichloromethane so as to obtain 6.3 g (yield of 79%)of 1,2,3,4,7,8,9,10,-octafluoro-6,11-dihydroxynaphthacene-5,12-dione(7).

Melting point: 300° C. (decomposition)

Mass spectrometry (MS m/z): 434 (M⁺, 100)

Elemental analysis

Calculated values for C₁₈H₂F₈O₄: C, 49.79, H, 0.49

Found values: C, 49.81, H, 0.57.

{1-2-1} Further to {1-1},1,2,3,4,5,5,6,6,7,8,9,10,11,11,12,12-hexadecafluoro-5,6,11,12-tetrahydronaphthacene(8) was synthesized from the obtained1,2,3,4,7,8,9,10-octafluoro-6,11-dihydroxynaphthacene-5,12-dione (7).

The obtained1,2,3,4,7,8,9,10-octafluoro-6,11-dihydroxynaphthacene-5,12-dione (7) (1g, 2.3 mmol) was thrown into a 200 mL autoclave made of SUS, thecontainer was cooled down to −78° C., hydrogen fluoride (56 g) wasadded, and, continuously, sulfur tetrafluoride (6.9 g, 64 mmol) wasadded. Subsequently, heating up to 150° C. was made on the condition ofsealing the reactor. At this time, the pressure in the reactor reachedat 3.2 MPa (gage pressure). After the reaction was made for 24 hours,the reactor was gradually cooled down to room temperature and a lowboiling point compound was slowly disposed to an exclusion device. Whenthe internal pressure reached at normal pressure, nitrogen wasintroduced into the container so that all the remaining hydrogenfluoride was removed, whereby 1.2 g of a mixture of1,2,3,4,5,5,6,6,7,8,9,10,11,11,12,12-hexadecafluoro-5,6,11,12-tetrahydronaphthacene(8) and a high boiling point product ((8): the high boiling pointproduct=70:30 (result of mass spectrometry)) was obtained. Afterward,the reaction product was purified by means of sublimation so as toobtain 0.425 g (0.82 mmol, yield of 36%) of a purified (8).

Melting point: 179-183° C.

¹⁹F NMR (188 MHz, solvent: CDCI₃, reference material: C₆F₆)

δ 71.90-71.78 (m, 8F), 25.64-25.44 (m, 4F), 16.30 (d, J=12.4 Hz, 4F)

Mass spectrometry (MS m/z): 520 (M⁺, 93), 501 (M⁺—F, 40), 451 (M⁺—CF₃,100), 432 (29), 413 (47.2), 401 (43), 382 (80)

Elemental analysis

Calculated values for C₁₈F₁₆: C, 41.56

Found values: C, 41.22.

{1-2-2}Further to {1-1},1,2,3,4,5,5,6,6,7,8,9,10,11,11,12,12-hexadecafluoro-5,6,11,12-tetrahydronaphthacene(8) and1,2,3,4,5,5,6,7,8,9,10,11,12,12-tetradecafluoro-5,12-dihydronaphthacene(9) were synthesized from the obtained1,2,3,4,7,8,9,10-octafluoro-6,11-dihydroxynaphthacene-5,12-dione (7).

The obtained1,2,3,4,7,8,9,10-octafluoro-6,11-dihydroxynaphthacene-5,12-dione (7) (1g, 2.3 mmol) was thrown into a 200 mL autoclave made of SUS, thecontainer was cooled down to −78° C., hydrogen fluoride (56 g) wasadded, and, continuously, sulfur tetrafluoride (5.4 g, 50 mmol) wasadded. Subsequently, heating up to 150° C. was made on the condition ofsealing the reactor. At this time, the pressure in the reactor reachedat 3.4 MPa (gage pressure). After the reaction was made for 4 hours, thereactor was gradually cooled down to room temperature and a low boilingpoint compound was slowly disposed to an exclusion device. When theinternal pressure reached at normal pressure, nitrogen was introducedinto the container so that all the remaining hydrogen fluoride wasremoved, whereby 1.1 g of a mixture of1,2,3,4,5,5,6,6,7,8,9,10,11,11,12,12-hexadecafluoro-5,6,11,12-tetrahydronaphthacene(8),1,2,3,4,5,5,6,7,8,9,10,11,12,12-tetradecafluoro-5,12-dihydronaphthacene(9) and a high boiling point product ((8):(9): the high boiling pointproduct=47:47:6 (result of mass spectrometry)) was obtained.

Mass spectrometry for (9) (MS m/z): 482 (M⁺, 100)

{1-3} Further to {1-2-1}, dodecafluoronaphthacene (10) was synthesizedfrom the obtained1,2,3,4,5,5,6,6,7,8,9,10,11,11,12,12-hexadecafluoro-5,6,11,12-tetrahydronaphthacene(8).

A mixture of the obtained1,2,3,4,5,5,6,6,7,8,9,10,11,11,12,12-hexadecafluoro-5,6,11,12-tetrahydronaphthacene(8) (426 mg, 0.82 mmol) and zinc (4.3 g, 66 mmol) was put into a glasstube (length of 100 mm, outer diameter of 26 mm), and the tube wassealed under vacuum and heated at 230° C. for 30 minutes andcontinuously at 280° C. for 3 hours. The reaction mixture was sublimedat 210° C. under vacuum, so as to obtain 197 mg (54%) ofdodecafluoronaphthacene (10).

Melting point: 318° C.

¹⁹F NMR (188 MHz, solvent: CDCl₃, reference material: C₆F₆)

δ 43.30-43.03 (m, 4F), 17.82-17.55 (m, 4F), 9.53-9.36 (m, 4F)

Mass spectrometry (MS m/z): 444 (M⁺, 100), 413 (M⁺—CF, 23), 375 (14),222 (32)

Elemental analysis

Calculated values for C₁₈F₁₂: C, 48.67

Found values: C, 48.54.

Additionally, in the above-mentioned synthesis ofdodecafluoronaphthacene, B-540 type of Büchi Company was used for themeasurements of melting point. For the NMR, Gemini 200 NMR Spectrometerof Varian Company was used. For the mass spectrometry, GCMS-QP5050A ofShimadzu Corporation was used. For the elemental analysis, CHN coderMT-6 type of Yanaco was used.

{2} Fabrication of an organic TFT Having an organic Semiconductor Layermade of dodecafluoronaphthacene

As a substrate for an organic TFT, a silicon wafer was used on thesurface of which thermally oxidized silicon with a film thickness of 200nm was formed. Herein, for the silicon wafer, a low resistive siliconwafer was used, and a silicon layer on the substrate also functioned asa gate electrode of the organic TFT. After the substrate was washed withorganic solvents such as acetone and isopropyl alcohol, the substratewas further washed by using an ultraviolet-ray-ozone washer. Also,according to need, the substrate was subjected to surface treatment byusing octadecyltrichlorosilane (OTS).

Next, the oxidized silicon film on the substrate was used as a gateinsulating-film and an organic semiconductor layer made ofdodecafluoronaphthacene was formed on the oxidized silicon film by meansof a vacuum deposition method using dodecafluoronaphthacene synthesizedin {1}. Herein, the organic semiconductor layer made ofdodecafluoronaphthacene was formed under the following conditions. Thedegree of vacuum in a chamber of the apparatus used in regard to thevacuum deposition method was 1×10⁻⁴ pascals or lower. The temperature ofthe substrate was in a range of room temperature (24° C.) or higher and80° C. or lower. The dodecafluoronaphthacene purified by means ofsublimation was thrown into a crucible made of carbon and thedodecafluoronaphthacene was heated by using a tantalum wire filamentwinding around the crucible. The deposition rate of the organicsemiconductor layer was 0.3 angstroms/second or higher and 0.5angstroms/second or lower and the film thickness was approximately 35nm.

Finally, gold layers with a film thickness of 50 nm were film-formed onthe organic semiconductor layer by means of a vacuum deposition methodusing a metal-mask, so as to form a source electrode and a drainelectrode. Herein, the channel width and channel length of an organicTFT obtained by forming the source electrode and the drain electrodewere 50 μm or greater and 200 μm or less, and 1,000 μm, respectively.

Thus, the organic TFT having an organic semiconductor layer made ofdodecafluoronaphthacene as shown in FIG. 1 could be fabricated.

{3} Measurement for the organic TFT Having an organic SemiconductorLayer Made of dodecafluoronaphthacene

X-ray crystallographic analysis was performed for the organicsemiconductor layer made of dodecafluoronaphthacene fabricated in {2}was performed. The X-ray used for the measurement of an X-raydiffraction pattern was a Cu—Kα line with a wavelength of 5.14angstroms. As an X-ray diffraction pattern obtained for the organicsemiconductor layer made of dodecafluoronaphthacene, the primary,secondary and tertiary peaks were observed which correspond to anintermolecular space of 13 angstroms. Based on the X-ray diffractionpattern corresponding to an intermolecular space of 13 angstroms, itcould be confirmed that the long axis directions of molecules ofdodecafluoronaphthacene were oriented along the vertical directions tothe surface of the substrate. Such a molecular orientation ofdodecafluoronaphthacene is preferable, since π-electronic orbitals ofthe molecules overlap with each other in directions parallel to thesurface of the substrate. Accordingly, it is deduced that carriersinduced in the organic semiconductor layer can comparatively easily moveto the directions parallel to the surface of the substrate. Also, it canbe understood that a thin film of dodecafluoronaphthacene in which thelong axis directions of the molecule are directed to the verticaldirections to the surface of the substrate is preferable for an organicsemiconductor layer of an organic TET, since a direction in which theπ-electronic orbitals of the molecules of dodecafluoronaphthaceneoverlap with each other corresponds to the direction of carrier movementfrom the source electrode to the drain electrode in the organic TFTshown in FIG. 1. Also, it can be understood that the spaces betweenmolecules of dodecafluoronaphthacene are comparatively uniform in a thinfilm of dodecafluoronaphthacene fabricated by controlling thetemperature of the substrate to approximately 24° C. or higher andapproximately 60° C. or lower, since the peak intensity of the X-raydiffraction pattern is comparatively strong and the peak half-valuewidth is comparatively small.

Next, the electrical characteristics of the organic TFT having anorganic semiconductor layer made of dodecafluoronaphthacene fabricatedin {2} were measured. As a result, at a gate voltage, a curve in regardto the change in the drain current versus the drain voltage was good andhad a linear region (voltage-proportional region) for low drain voltagesand a saturation region for high drain voltages. In addition, when apositive gate voltage applied to the gate electrode was increased, apositive drain current was also increased, and, therefore, it could beconfirmed that the organic TFT having an organic semiconductor layermade of dodecafluoronaphthacene fabricated in {2} was an n-type organicTFT. Further, the field-effect mobility μ of carrier of the organic TFThaving an organic semiconductor layer made of dodecafluoronaphthacenefabricated in {2} was calculated by using the above formula (A) whichrepresents a drain current Id in a saturation region in regard to theelectrical characteristics of an organic TFT and, as a result, thefield-effect mobility of carrier of the organic TFT having an organicsemiconductor layer made of dodecafluoronaphthacene fabricated at asubstrate temperature of 40° C. was 0.01 cm²/Vs.

The embodiments and practical examples of the present invention havebeen specifically described above, but the present invention is notlimited to these embodiments and practical examples and theseembodiments and practical examples of the present invention can bemodified or altered without departing from the spirit and scope of thepresent invention.

INDUSTRIAL APPLICABILITY

The present invention can be applied to an organic thin-film transistorhaving a higher carrier-mobility, a method of fabricating the organicthin-film transistor and an organic thin-film device including theorganic thin-film transistor.

1. A method of fabricating an organic thin-film transistor comprising asubstrate and an organic semiconductor layer, wherein the organicsemiconductor layer is obtained by controlling temperature of thesubstrate to 30° C. or higher and 65° C. or lower and vacuum-depositingtetradecafluoropentacene (C₂₂F₁₄) on the substrate at 1×10⁻⁴ pascals orlower.
 2. A method of fabricating an organic thin-film transistorcomprising a substrate and an organic semiconductor layer, wherein theorganic semiconductor layer is obtained by controlling temperature ofthe substrate to 24° C. or higher and 60° C. or lower andvacuum-depositing dodecafluoronaphthacene (C₁₈F₁₂) on the substrate at1×10⁻⁴ pascals or lower.
 3. An organic thin-film transistor comprising asubstrate and thin films of gate electrode, gate insulating film,organic semiconductor layer, and source and drain electrodes stacked onthe substrate in order, wherein the thin film of organic semiconductorlayer is obtained by controlling temperature of the substrate to 24° C.or higher and 60° C. or lower and vacuum-depositingdodecafluoronaphthacene (C₁₈F₁₂) on the substrate at 1×10⁻⁴ pascals orlower.